1. Field of the Invention
The invention is related to the field of flow meters, and in particular, is related to detecting a residual material in a flow meter assembly of a flow meter.
2. Statement of the Problem
Flowmeters are used to measure the mass flow rate, density, and other characteristics of flowing materials. The flowing materials can comprise liquids, gases, combined liquids and gases, solids suspended in liquids, and liquids including gases and suspended solids. For example, flowmeters are used in industrial processes for measuring quantities of ingredients and resultant products by measuring a flow rate (i.e., by measuring a mass flow through the flowmeter).
One type of flow meter is a Coriolis flow meter. It is known to use Coriolis mass flow meters to measure mass flow and other information of materials flowing through a pipeline as disclosed in U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al. of Jan. 1, 1985 and Re. 31,450 to J. E. Smith of Feb. 11, 1982. These flow meters have one or more flow tubes of different configurations. Each conduit configuration may be viewed as having a set of natural vibration modes including, for example, simple bending, torsional, radial and coupled modes. In a typical Coriolis mass flow measurement application, a conduit configuration is excited in one or more vibration modes as a material flows through the conduit, and motion of the conduit is measured at points spaced along the conduit. The vibrational modes of the material filled systems are defined in part by the combined mass of the flow tubes and the material within the flow tubes. When there is no material flowing through the flow meter, all points along a flow tube oscillate with an identical phase. As a material begins to flow through the flow tube, Coriolis accelerations cause each point along the flow tube to have a different phase with respect to other points along the flow tube. The phase on the inlet side of the flow tube lags the driver, while the phase on the outlet side leads the driver. Sensors are placed at different points on the flow tube to produce sinusoidal signals representative of the motion of the flow tube at the different points. A phase difference of the signals received from the sensors is calculated in units of time. The phase difference between the sensor signals is proportional to the mass flow rate of the material flowing through the flow tube or flow tubes.
A problem exists in the prior art in determining whether any residual material remains in a flow meter. When a flow meter is allowed to self-drain, some moisture may remain within a flow tube. This is especially true in a closed environment. The flow meter may comprise a flow meter that employs a straight flow tube apparatus, wherein an amount of residual material can remain in the flow tube apparatus and not drain. Alternatively, a flow meter may employ an arc or loop-shaped flow tube apparatus. The shape of such a flow tube apparatus can trap a significant amount of residual material and can present additional challenges in ensuring that a process fluid has totally drained from the flow meter. In addition, the installation orientation of the flow meter can contribute to retention of residual material, wherein the residual material is unable to adequately or completely drain out of the flow meter.
In some applications, particularly within the pharmaceutical, biotech, and food and beverage industries, it is critical to ensure that a flow meter has totally self-drained and is free of flow media.